Simpler and more rapid color development processing, high picture quality and uniformity of finish are desirable characteristics of color photosensitive materials.
In order to speed up color development processing it is necessary to speed up two types of reactions including the reaction between the silver halide grains and the color developer and the subsequent reaction which takes place between the color couplers and the oxidation products of the developing agents thus formed.
In the reaction between silver halide grains and the color developer, it is known that the form, size and composition of the photosensitive silver halide grains used have a considerable effect on the rate of development.
It is also known in this connection that silver chloride grains and grains which have a high silver chloride content in particular are useful for speeding up development.
The coupling activity of the coupler is a dominant factor in the development rate, especially in cases where benzyl alcohol is not used in the developer due to environmental concerns.
Many attempts have been made recently to increase the rate of development using high silver chloride content emulsions in color development baths which do not contain benzyl alcohol.
However, although it is possible to increase the rate of development using these techniques, few proposals have been made in connection with the provision of photosensitive materials having high silver chloride content emulsions to be manufactured on a commercial basis and in a stable manner. Current techniques are not be adequate in this regard.
High silver chloride emulsions are very effective for rapid processing, especially with development baths which do not contain benzyl alcohol, but mass production in a stable manner is very difficult.
This difficulty in manufacturing is explained as follows: such emulsion coating liquids are prepared by mixing dispersions of color couplers in high boiling point organic solvents with spectrally sensitized high silver chloride content emulsions. A certain time elapses before these mixtures are coated onto the support. It is difficult to maintain a constant lapse time between preparation of the emulsion coating liquid and subsequent coating on the support in the type of facility normally used for the mass production of photographic materials. This variation in coating time is related to a fluctuation in photographic performance.
Fluctuation in photographic performance occurs when emulsion coating liquids are left to stand prior to coating because adsorption of the spectrally sensitizing dyes on the high silver chloride content emulsion is affected by the dispersion of the color coupler and the high boiling point organic solvent mixture. High silver chlolide content emulsions have a much weaker affinity for spectrally sensitizing dyes as compared to emulsions which have a high silver bromide content.
Consequently, the use of spectrally sensitizing dyes which are more strongly adsorbed on high silver chloride emulsion grains has been suggested as a means of resolving the above problems. These techniques have been disclosed in practical terms in JP-A-59-166955 and JP-A-59-214030 for example (the "JP-A" as used herein signifies a published, unexamined Japanese patent application).
However, the selection of sensitizing dyes which do not result in fluctuation in photographic performance, even in the mass production of photosensitive materials with high silver chloride content emulsions, is quite difficult for the reasons described below.
Spectrally sensitizing dyes affect many aspects of photographic performance including exposure luminance dependence of the photographic emulsion speed, latent image storage properties and stability on storage of the product for prolonged periods of time in addition to basic intensity and wavelength band of the spectral sensitization. Sensitizing dyes which have adequate adhesion on high silver chloride grains do not always meet all of the above performance requirements and indeed, such cases are in fact rather rare.
Fluctuation in performance arising from variation in coating time of a mixture of a spectrally sensitized high silver chloride content emulsion and a mixed dispersion of color couplers and high boiling point organic solvent strongly affects photographic properties.
Photosensitive materials which exhibit a dependency of the type referred to above are generally susceptible to similar fluctuations in performance once the samples have been coated.